This document relates to using a cavity to polarize a spin ensemble for magnetic resonance imaging (MRI).
In magnetic resonance systems, signal-to-noise ratio (SNR) generally depends on the spin polarization and the time required to reach thermal equilibrium with the environment. The time required to reach thermal equilibrium—characterized by the energy relaxation time T1—often becomes long, for example, at low temperatures. Conventional techniques for removing entropy from a quantum system include dynamic nuclear polarization (DNP), algorithmic cooling, optical pumping, laser cooling, and microwave cooling, among others.
Various approaches have been used to increase the signal-to-noise ratio (SNR) in magnetic resonance applications. For instance, signal averaging over multiple acquisitions is often used to increase SNR. Another approach is to increase the induction probe sensitivity, for example, by overlapping multiple induction coils and using phased array techniques. In some systems, induction probes are embedded in cryogens to reduce intrinsic noise within the induction probes.